Integrating amplifier



Sept. 23, 1958 M. A. ALEXANDER 2,853,607

INTEGRATING AMPLIFIER Filed Aug. 25. 1954 '0 TRIGGIR- 0Y6 SAG/Vii JOURCEBy Agog/70% ATTOR/VEIS The anode voltage slowly decreases in value.

United States PatentD INTEGRATING AMPLIFIER Matthew Arnold Alexander,Pacific Palisades, Califl, as-

signor, by mesne assignments, to Telemeter Magnetics and ElectronicsCorporation, Los Angeles, Caiifl, a corporation of New York ApplicationAugust 23, 1954, Serial No. 451,383 5 Claims. I (Cl. 250-27 Thisinvention relates to electronic amplifier networks and more particularly'to an improvement in electronic integrating networks. Integratingnetworks find extensive use in present-day electronic systems ascomponents in analogue computers. Furthermore, in view of thesubstantial linearity of their output wave shape, they also findextensive use for the provision of accurate timing wave shapes. TheMiller integrator usually consists of an electron discharge tube withits anode connected back toits grid by way of a condenser. This negativefeedback is provided to the grid. Input signals are applied to the gridthrough a resistor. In operation, the integrator tube is biased in theconducting region. A positive input to the grid increases the tube anodecurrent. The longer the duration of'the application of the positiveimpulse, the more toward conduction a tube is driven. The negativefeedback from -the anode prevents instantaneous conduction but makesthis a function of the values of input resistor and feedback condenserand the duration of the application of the positive input pulse. Thewave shape obtained from the anode is essentially a time integral of theinput signal. For a given constant input voltage signal the slope of thevoltage output curve is substantially constant. In order to insureisolation between the integrating tnbe and its output load, a cathodefollower may be employed in the feedback loop. The output from the anodeof the integrator tube is applied to the control grid of acathode-follower tube. The integrating condenser couples thecathode-follower cathode with the control grid of the integrator tube.Output is taken from the cathode-follower cathode. It will beappreciated that the higher the gain of the integrator tube, the greaterthe feedback voltage for a given signal and the more linear will be theoutput wave shape and the less the possibility for variation thereofwith variation of the circuit components.

An object of the present invention is to provide a novel high-gainintegrating network.

High gain may be achieved by increasing the anode load of the integratortube. However, this has the disadvantage of requiring a high value ofanode load supply voltage.

Accordingly, another object of the present invention is to increase thegain of an integrating circuit by increasing the effective value of theanode load resistance and anode supply voltage.

Still another object of the present invention is to provide a novel,simple, and stable high-gain integrating circuit.

These and other features of the invention are achieved in an integratingcircuit of the type employing a cathode follower in its feedback loop byusing a voltage regulator tube or tubefilled with inert gas which isconnected between the cathode of the cathode follower and a tap on theanode load circuit.

The novel features that are considered characteristic of this inventionare set forth with particularity in the ap- A ice grid 14, cathode 20,screen grid 16, and suppressor grid I 18. An operating voltage supply isprovided. A voltage divider 22 is connected across the voltage supplyfor the purpose of providing a voltage for the screen grid'1 6 which isconnected to it. This is maintained relatively low. The suppressor grid18 maybe utilized for maintaining the first tube cut off until it isdesired to operate the integrator network for which purpose it may beconnected to a source of triggering signals. Otherwise, it

may be connected to ground. The cathode 20 of the first tube isconnected to ground. The anode 12 is connected through twoseries-connected anode load resistors 24,

I which may also be a single anode load resistor 24 with a tap, to thesource of operating voltage. A second tube 30, which is acathode-follower tube, has its control grid 32 directly connected to theanode 12 of the first tube. Its anode 34 is connected to the source ofoperating potential and a cathode load resistor 38 connects its cathode36 to a source of negative bias. A feedback condenser 40 connects thecathode-follower cathode to the control grid of the integrator tube. Aninput signal is applied through an input resistor 42 which is connectedto the control grid 14.

As thus far described, this system is a well-known type of integratorwith feedback using a cathode-follower tube. As the anode of the firsttube goes positive or negative in response to an input signal, acorresponding positive or negative voltage is fed to the first tubecontrol grid through the cathode-follower tube and the couplingcondenser. The theory of these integrating networks may be founddescribed, for example, in chapter 4 of the book Electronic Instrumentsby Greenwood et al., published by McGraw-Hill Book Company.

With a given power supply and tube type, in order'to increase the tubegain or the change of voltage at the anode in response to a change inthe signal applied to the control grid, the value of the anode loadresistor is increased. Thereby, changes in current drawn by the tube asa result of the signals applied to the control grid pro duce largervoltage changes at the anode. However, a point of diminishing returns israpidly approached, since the increased anode load resistor lowers thevoltage available at the tube anode. Accordingly, the tube draws lesscurrent and the gain is actually less than more. With the presentinvention, an increase in the gain available from the first tube issecured by connecting a gas-filled diode or neon-glow tube which isgenerically referred to here as a voltage-regulator tube 50 between thetapped anode load resistor 24 and the cathode 36 of the cathodefollowertube. The tapping point is selected so that the potential across thetube exceeds its required ignition voltage. The anode 52 is connected tothe anode load resistor and the cathode 54 is connected to thecathodefollower cathode. This has the effect of making the gain of thesystem exceedingly high. This will be seen from the followingexplanation of the operation of the invention.

Assume, for the purposes of explanation, that the voltage at the anodeof the tube is volts. The voltageat the junction of the two anode loadresistors is 187 volts, there being an 87-volt drop across the lowermostportion of the load resistor as a result of the current flowing throughthe first tube. The voltage applied to the grid of the cathode followeris substantially 100 volts,

and the voltage at the cathode of the cathode follower may be a fewvolts more than this value. Accordingly, the voltage being applied tothe control grid of the tube is also substantially 100 volts. Thevoltage across the. voltage regulator tube is essentially 87 volts,which is sufiicient to make it conductive. Assume a signal is appliedthrough the input resistor to the control grid o the integrator tube,which causes the tube to draw more current. Assume that this signalcauses, a lO-volt drop at the anode of the first tube. to occur at thegrid of the cathode follower and substantially a IO-volt drop at thecathode of the cathode follower. Since there is a constant voltage dropacross the regulator tube, there occurs a 10-volt drop at the junctionof the two anode load resistors. There is a 10-volt drop. if (1) thegain of the cathode follower is unity and (2.) the efiective resistanceof the regulator tube is zero. The effect of (1) a finite regulatorimpedance, (2) a gain of less than unity in the cathode follower, andv(3) the finite impedance of the tube 10 is to reduce the value of the,voltage fed back to the junction of the two anode resistors. The changein current in the section of resistor 24 between the plate of tube 50and the plate of tube 10- has been decreased from the value without thisform of positive feedback to a value where A is, a number whichprimarily specifies the gain of the cathode follower. The value of A mayapproach one very nearly say .99. Using this value of A as an example,the efiective value of R has been increased by 100 times and theeffective potential applied to R has been increased 100 times. Thecircuit behaves similarly if the input voltage is such as to cause anincrease of Voltage at the anode.

Therefore, the effect of the connection of the voltage regulator tubeinto the integrator network is to provide an extremely high-gainintegrator network with-out increasing the first tube anode loadresistor, without increasing the voltage from the power supply orchanging the type of tube used. Despite the large amount of positivefeedback, there is no oscillation since, in view of the cathodefollower, the feedback loop gain is less than one, although the systemgain is extremely high, gains on the order of 100,000 having beenachieved.

Thus, with a simple expedient, this invention achieves a novel, useful,and simple high-gain integrating network that can provide a very stableand linear output in response to an input signal.

I claim:

1. In an electronic integrator of the type having a first tube includingan anode and a control grid, an anode load resistor connected to saidanode, a feedback network between said first tube anode and control gridincluding a cathode follower tube having a control grid and cathode,said control grid being connected to said first tube anode, and acondenser connected between said cathode-follower This causes a 10-voltdrop a cathode and said first control grid, the improvement consistingof a voltage regulator tube connected between a point on said anode loadresistor and said cathode-follower cathode.

2. In an electronic integrator as recited in claim 1 wherein saidvoltage regulator tube has an anode and cathode, said anode beingconnected to the tapon said anode load resistor and said cathode being.connected to the cathode of said cathode follower tube.

3. An electronic integrating network consisting of a first and a secondtube each having anode, cathode and'control grid electrodes, meansconnecting said first tube anode to said second tube control grid, acathode load resistor connected to said second tube-cathode, an anodeload resistor connected to said first tube anode, a condenser connectedbetween said second tube cathode and said first tube control grid, asignal input resistor connected to said control grid, and a voltageregulator tube connected between a tap on said anode load resistor andsaid second tube cathode.

4. The combination with an electronic integrator of'the type having afirst tube including an anode and a control grid, an anode load resistorconnected to saidanode, a feedback network between said first tube anodeand control grid including a cathode-follower tube having a controlgrid'and cathode, said control grid being connected to said first tubeanode, and a condenser connected between said cathode-follower cathodeand said first tube control grid, of a voltage regulator tube having ananode anda cathode, said voltage regulator anode beingc'onnected to apoint on said anode load resistor, said voltage regulator cathode beingconnected to said cathode-follower cathode.

5. An electronic integrating network consisting of a first tube havingan anode and a control grid, an anode load resistor connected to saidanode, and a feedback network between said anode and said control grid,said feedback network including a cathode-follower tube, saidcathode-follower tube having a cathode and control grid, saidcathode-follower tube control grid being connected to said first tubeanode, said cathode-follower tube cathode; being coupled to said firsttube control grid, a voltage-regulator tube having an anode and acathode, said voltageregulator tube cathode being coupled to saidcathode-follower tube cathode, and said voltage-regulator tube anodebeing connected to a point on said first tube anode load resistor thepotential at which exceeds the potential at said cathode-follower gridby an amount sufficient to render said voltage-regulator tubeconducting.

References Cited in the file of this patent UNITED STATES PATENTS2,554,172 Custin May 22, 1951 2,562,792 James July 31, 1951 2,581,456Swift Jan. 8, 1952 2,642,532 Mofenson June 16, 1953 2,651,719 WhiteSept. 8, 1953. 2,662,981 Segerstrom Dec. 15, 1953 2,678,391 Lappin May11, 1954 2,691,728 Noble et al. Oct. 12, 1954 2,701,306 Bess Feb. 1,1955 2,769,904 Ropiequet Nov. 6, 1956

